1. Field of the Invention
The invention relates to a plasma display apparatus having a plasma display panel.
2. Description of the Related Art
In recent years, a thin type display device has been requested associated by the realization of a large screen of a display apparatus and various thin type display devices have been put into practical use. Attention is paid to a plasma display panel of an AC discharge type as one of the thin type display devices.
FIG. 1 is a diagram showing a construction of a plasma display apparatus having a plasma display panel (designated as a PDP hereinafter).
In FIG. 1, a PDP 10 comprises: m column electrodes D1 to Dm; and n row electrodes X1 to Xn and n row electrodes Y1 to Yn which are arranged so as to cross the column electrodes, respectively. With respect to the row electrodes X1 to Xn and the row electrodes Y1 to Yn, first to nth display lines in the PDP 10 are constructed by pairs of row electrodes Xi (1xe2x89xa6ixe2x89xa6n) and Yi (1xe2x89xa6ixe2x89xa6n). A discharge space filled with discharge gas is formed between the column electrode D and the row electrodes X and Y. The discharge space has a structure such that a discharge cell serving as a display pixel is formed at a crossing portion of each row electrode pair and the column electrode.
Each discharge cell has only two states of xe2x80x9clight emissionxe2x80x9d and xe2x80x9cnon-light emissionxe2x80x9d because a light emission is performed by using a discharge phenomenon. That is, only luminance of two gradations of the lowest luminance (non-light emitting state) and the highest luminance (light emitting state) is realized.
A driving apparatus 100, therefore, executes a gradation driving using a subfield method in order to allow the PDP 10 to realize a luminance display of a halftone corresponding to a supplied video signal. As subfield methods, there are a selective erasure address method and a selective write address method. According to the selective erasure address method, wall charges are previously formed in all discharge cells (all-resetting step Rc) and the wall charges in each discharge cell are selectively erased in response to an input video signal (pixel data writing step Wc). According to the selective write address method, wall charges in all discharge cells are previously extinguished (all-resetting step Rc) and the wall charges are selectively formed in each discharge cell in response to an input video signal (pixel data writing step Wc).
In the subfield method, the supplied video signal is converted into pixel data of, for example, 4 bits corresponding to each pixel and one field is divided into four subfields SF1 to SF4 as shown in FIG. 2 in correspondence to each bit digit of the 4 bits. At this time, as shown in FIG. 2, the number of executing times of light emission corresponding to a weight of the pixel data bits is allocated to each of the subfields SF1 to SF4. The discharge cells are light-emitted every subfield in accordance with a logic level of the pixel data bit corresponding to the subfield.
FIG. 3 is a diagram showing various kinds of driving pulses which are applied to the row electrode pairs and the column electrodes of the PDP 10 in one subfield in order to drive the driving apparatus 100 by, for example, the selective erasure address method and showing timing for applying those pulses.
First, in the all-resetting step Rc, the driving apparatus 100 applies a reset pulse RPx of a negative polarity whose trailing change is mild and which is shown in FIG. 3 all at once to each of the row electrodes X1 to Xn. The driving apparatus 100, further, applies a reset pulse RPY, of a positive polarity whose leading change is mild and which is shown in FIG. 3 all at once to each of the row electrodes Y1 to Yn simultaneously with the application of the reset pulse PRX. In accordance with the application of the reset pulses RPX and RPY, all of the discharge cells of the PDP 10 are discharged for resetting. After termination of the reset discharge, wall charges of a predetermined amount are uniformly formed in each discharge cell and the formed wall charges are held.
By the execution of the all-resetting step Rc, all of the discharge cells in the PDP 10 are initialized to a state where a light emission (sustaining discharge) is possible (hereinafter, referred to as a xe2x80x9clight emitting cellxe2x80x9d state) in a light emission sustaining step Ic, which will be explained hereinlater.
In the pixel data writing step Wc, the driving apparatus 100 separates each bit of the pixel data of 4 bits in correspondence to each of the subfields SF1 to SF4 and generates a pixel data pulse having a pulse voltage according to a logic level of the bit. For example, in the pixel data writing step Wc of the subfield SF1, the driving apparatus 100 generates the pixel data pulse having the pulse voltage according to the logic level of the first bit of the pixel data. At this time, the driving apparatus 100 generates the pixel data pulse having the pulse voltage of a high voltage if the logic level of the first bit is equal to xe2x80x9c1xe2x80x9d and generates the pixel data pulse having the pulse voltage of a low voltage (0 volt) if the logic level of the first bit is equal to xe2x80x9c0xe2x80x9d. The driving apparatus 100 sequentially applies the pixel data pulses as pixel data pulse groups DP1 to DPn as many as each display line corresponding to each of the first to nth display lines to the column electrodes D1 to DM as shown in FIG. 3. The driving apparatus 100, further, generates a scanning pulse SP of a negative polarity as shown in FIG. 3 synchronously with the applying timing of each of the pixel data pulse groups DP and sequentially applies the scanning pulse to the row electrodes Y1 to Yn. At this time, a discharge (selective erasure discharge) is caused only in the discharge cell at the crossing portion of the display line to which the scanning pulse SP has been applied and the xe2x80x9ccolumnxe2x80x9d to which the pixel data pulse of the high voltage has been applied. By the selective erasure discharge, the wall charges held in the discharge cell are extinguished. That is, the discharge cell is shifted to a state where the light emission (sustaining discharge) is impossible (hereinafter, referred to as a xe2x80x9cnon-light emitting cellxe2x80x9d state) in the light emission sustaining step Ic, which will be explained hereinlater. The selective erasure discharge is not caused in the discharge cell to which the pixel data pulse of the low voltage has been applied although the scanning pulse SP was applied. That is, the discharge cell sustains the state where it has been initialized in the all-resetting step Rc, that is, the xe2x80x9clight emitting cellxe2x80x9d state.
That is, according to the pixel data writing step Wc, each discharge cell of the PDP 10 is set to either the xe2x80x9clight emitting cellxe2x80x9d state or the xe2x80x9cnon-light emitting cellxe2x80x9d state in accordance with the pixel data based on the input video signal.
Subsequently, in the light emission sustaining step Ic, the driving apparatus 100 alternately and repetitively applies a sustaining pulse IPX of a positive polarity and a sustaining pulse IPY of a positive polarity to the row electrodes X1 to Xn and the row electrodes Y1 to Yn as shown in FIG. 3. In one subfield, the number of times (period) of applying the sustaining pulses IPX and IPY is set in accordance with a weight of each subfield as shown in FIG. 2. Only the discharge cell in which the wall charges exist, namely, only the discharge cell in the xe2x80x9clight emitting cellxe2x80x9d state discharges for the sustaining light emission each time the sustaining pulses IPX and IPY are applied. That is, only the discharge cell set to the xe2x80x9clight emitting cellxe2x80x9d state in the pixel data writing step Wc repeats the light emission associated by the sustaining discharge the number of times set in correspondence to the weight of each subfield as shown in FIG. 2 and sustains the light emitting state.
The driving apparatus 100 executes the above operation every subfield. In this instance, a luminance of the halftone corresponding to the video signal is expressed by the total number (in one field) of light emissions associated by the sustaining discharge caused in each subfield. That is, the image display corresponding to the video signal is performed by the light emission caused by the sustaining discharge.
To perform the image display by using a discharge phenomenon, however, a discharge which causes a light emission that is not concerned with the display image has to be also caused. Particularly, since all of the discharge cells perform the light emission all at once by a reset discharge which is caused in the all-resetting step Rc, a problem such that a decrease in contrast appears typically when an image of a low luminance is displayed occurs. To prevent the problem, as shown in FIG. 3, each of the trailing change of the reset pulse RPx which is applied to cause the reset discharge and the leading change of the reset pulse RPY which is also applied is set to be mild. Although the amount of light emission associated by the reset discharge consequently decreases, an amount of wall charges and priming particles which are formed also decreases. At this time, in order to form a desired amount of wall charges and priming particles, it is necessary to increase pulse voltages (VR, xe2x88x92VR) of the reset pulses (RPY and RPX) and, further, widen a pulse width (TR) of each of them. A driver of a high withstanding voltage, therefore, is used as a driver for generating the reset pulses, resulting in an increase in costs. Further, if the pulse width of the reset pulse is widened, since a time which is necessary for the all-resetting step Rc becomes long, a time which is necessary for the pixel data writing step Wc and the light emission sustaining step Ic has to be shortened by the duration corresponding to it. An erroneous discharge, however, occurs if the pulse width of each of the pixel data pulse and the scanning pulse SP is narrowed in order to shorten the time which is necessary for the pixel data writing step Wc. The luminance of the whole picture plane decreases if the number of executing times of the sustaining discharge is decreased in order to shorten the time which is necessary for the light emission sustaining step Ic. That is, a problem of deterioration of the picture quality is caused.
The invention is made to overcome the above problems. An object of the invention is to provide a method for driving a PDP and a plasma display apparatus which can realize high picture quality and low costs.
According to a fist aspect of the invention, we provide a method for driving a PDP in accordance with video signals, said PDP including a plurality of discharge cells arranged in a matrix form, each of said discharge cells working as a display pixel. The method comprises the steps of: applying a reset pulse to all of said discharge cells to cause all of said discharge cells to discharge for resetting all of said discharge cells; applying a scanning pulse to each of said discharge cells to cause each of said discharge cells to selective-discharge for selecting either of light-emission and non-light-emission modes for each of said discharge cells on the basis of pixel data corresponding to a video signal for each of said discharge cells; and applying a sustaining pulse to allow only the discharge cell in the light-emission mode to discharge for repeating light emission. The reset pulse comprises a first pulse voltage shift interval in which a pulse voltage changes gradually, reaches a minimum reset-discharge starting voltage, and exceeds the minimum reset-discharge starting voltage, and a second pulse voltage shift interval in which said pulse voltage changes steeply.
According to a second aspect of the invention, we provides a method for driving a PDP in accordance with video signals, said PDP including a plurality of discharge cells arranged in a matrix form, each of said discharge cells working as a display pixel. The method comprises the steps of: applying a reset pulse to all of said discharge cells to cause all of said discharge cells to discharge for resetting all of said discharge cells; applying a scanning pulse to each of said discharge cells to cause each of said discharge cells to selective-discharge for selecting either of light-emission and non-light-emission modes for each of said discharge cells on the basis of pixel data corresponding to a video signal for each of said discharge cells; and applying a sustaining pulse to allow only the discharge cell in the light-emission mode to discharge for repeating light emission. The reset pulse comprises a first pulse voltage shift interval in which a pulse voltage changes steeply, and a second pulse voltage shift interval during which said pulse voltage changes gradually, reaches a minimum reset-discharge starting voltage, and exceeds the minimum reset-discharge starting voltage.
According to a third aspect of the invention, we provide a method for driving a PDP in accordance with video signals, said PDP including a plurality of discharge cells arranged in a matrix form, each of said discharge cells working as a display pixel. The apparatus comprises the steps of: applying a reset pulse to all of said discharge cells to cause all of said discharge cells to discharge for resetting all of said discharge cells; applying a scanning pulse to each of said discharge cells to cause each of said discharge cells to selective-discharge for selecting either of light-emission and non-light-emission modes for each of said discharge cells on the basis of pixel data corresponding to a video signal for each of said discharge cells; and applying a sustaining pulse to allow only the discharge cell in the light-emission mode to discharge for repeating light emission. The reset pulse comprises a first pulse voltage shift interval during which a pulse voltage changes steeply, a second pulse voltage shift interval during which said pulse voltage changes gradually, reaches a minimum reset-discharge starting voltage, and exceeds the minimum reset-discharge starting voltage, and a third pulse voltage shift interval during which said pulse voltage changes steeply.
According to a forth aspect of the invention, we provide an apparatus for driving a PDP in accordance with video signals, said PDP comprising a plurality of discharge cells arranged in a matrix form, each of said discharge cells working as a display pixel. The apparatus further comprises: a reset pulse generator for generating a reset pulse for causing each of said discharge cells to discharge and applying said reset pulse to all of said discharge cells, thereby resetting all of said discharge cells; a scanning pulse generator for generating a scanning pulse for causing each of said discharge cells to selective-discharge for selecting either of light-emission and non-light emission modes for each of said discharge cells in accordance with pixel data corresponding to a video signal for said each of discharge cells, and applying said scanning pulse to said each of discharge cells; and a sustaining pulse generator for generating a sustaining pulse to allow only the discharge cell in the light-emission mode to discharge for repeating light emission. The reset pulse comprises a first pulse voltage shift interval during which a pulse voltage changes gradually, reaches a minimum reset-discharge starting voltage, and exceeds said minimum reset-discharge starting voltage, and a second pulse voltage shift interval during which said pulse voltage changes steeply.
According to a fifth aspect of the invention, we provide an apparatus for driving a PDP in accordance with video signals, said PDP comprising a plurality of discharge cells arranged in a matrix form, each of said discharge cells working as display pixels. The apparatus further comprises: a reset pulse generator for generating a reset pulse for causing each of said discharge cells to discharge and applying said reset pulse to all of said discharge cells, thereby resetting all of said discharge cells; a scanning pulse generator for generating a scanning pulse for causing each of said discharge cells to selective-discharge for selecting either of light-emission and non-light emission modes for each of said discharge cells in accordance with pixel data corresponding to a video signal for said each of discharge cells, and applying said scanning pulse to said each of discharge cells; and a sustaining pulse generator for generating a sustaining pulse to allow only the discharge cell in the light-emission mode to discharge for repeating light emission. The reset pulse comprises a first pulse voltage shift interval during which a pulse voltage changes steeply, and a second pulse voltage shift interval during which said pulse voltage changes gradually, reaches a minimum reset-discharge starting voltage, and exceeds the minimum reset-discharge starting voltage.
According to a sixth aspect of the invention, we provide an apparatus for driving a PDP in accordance with video signals, said PDP comprising a plurality of discharge cells arranged in a matrix form, each of said discharge cells working as a display pixel. The apparatus further comprises: a reset pulse generator for generating a reset pulse for causing each of said discharge cells to discharge and applying said reset pulse to all of said discharge cells, thereby resetting all of said discharge cells; a scanning pulse generator for generating a scanning pulse for causing each of said discharge cells to selective-discharge for selecting either of light-emission and non-light emission modes for each of said discharge cells in accordance with pixel data corresponding to a video signal for said each of discharge cells, and applying said scanning pulse to said each of discharge cells; and a sustaining pulse generator for generating a sustaining pulse to allow only the discharge cell in the light-emission mode to discharge for repeating light emission. The reset pulse comprises a first pulse voltage shift interval during which a pulse voltage changes steeply, a second pulse voltage shift interval during which said pulse voltage changes gradually, reaches a minimum reset-discharge starting voltage, and exceeds said minimum reset-discharge starting voltage, and a third pulse voltage shift interval during which the pulse voltage changes steeply.
As mentioned above, according to the driving method of the PDP of the invention, the pulse comprising the interval where the pulse voltage is gradually shifted and the interval where it is steeply shifted is generated as a reset pulse which is applied for allowing the discharge cells of the PDP to be reset-discharged. In the invention, in the interval where the pulse voltage is gradually shifted, the pulse voltage is allowed to reach the minimum reset discharge starting voltage. Although the weak reset discharge of the low light emission luminance is, consequently, caused within the relatively short period of time, the applied voltage and the time which are necessary for forming the wall charges can be obtained.
According to the invention, therefore, since the desired amount of wall charges can be formed in each discharge cell without needing to increase the pulse voltage and pulse width of the reset pulse, the relatively cheap driver of a low withstanding voltage can be used as a driver for generating the reset pulse. Further, since the pulse width of the reset pulse can be narrowed more than that of the conventional pulse, the time which is used for the pixel data writing step and the light emission sustaining step can be extended by the time corresponding to it and the high picture quality can be realized.